A unique opportunity for studying embryonic determination and induction is afforded by the diverse differentiation of neural crest cells. The research proposed here examines the causal events underlying development of adrenergic neurons, a crest derivative. The objectives are as follows: (1) to test whether crest cells, before migration, are equivalent in their potentialities; (2) to extend previous studies of tissue interactions that induce and/or realize the adrenergic phenotype; and (3) to characterize morphological and biosynthetic responses of the crest cells to these inductive stimuli. Pluripotentiality will be examined by cloning single crest cells and testing the capacity of equivalent daughter cells to contribute to one or more crest derivatives. Tissues implicated in adrenergic neuroblast development include the somites and possibly the ventral half of the neural tube. Several lines of evidence suggest that the ventral neural tube may not be directly involved in these interactions. This question and also the nature of the somitic influence(s) will be examined. Work is proposed to evaluate crest-somite interactions that possibly affect enzymes in the noradrenaline pathway, manufacture of densecore storage granules and acquisition of catecholamine-uptake properties by crest cells.